U.S. patent number 3,955,017 [Application Number 05/272,498] was granted by the patent office on 1976-05-04 for method of coating metal phosphates on organic polymeric substrates.
This patent grant is currently assigned to Imperial Chemical Industries Limited. Invention is credited to Neville Colebourne, Kevin Thomas McAloon, Michael Leslie Orton, Nicholas Rolfe.
United States Patent |
3,955,017 |
Colebourne , et al. |
May 4, 1976 |
Method of coating metal phosphates on organic polymeric
substrates
Abstract
An organic polymer article has a surface coating of a metal
phosphate. The coating has a thickness in the range of 0.01 to 5
microns; preferably, the metal phosphate comprises a mixture of
iron and titanium orthophosphate, although the metal may be chosen
from the elements of a periodic table having an atomic number of
12, 14, 20 to 32, 39 to 50, 56 to 80, 90 or 92. A continuous
coating of the metal phosphate is obtained by applying to the
organic polymer article a solution of a compound of the metal
wherein the solution contains an organic component. The solution is
converted to the coating of the metal phosphate by drying.
Inventors: |
Colebourne; Neville (Runcorn,
EN), Rolfe; Nicholas (Runcorn, EN),
McAloon; Kevin Thomas (Runcorn, EN), Orton; Michael
Leslie (Runcorn, EN) |
Assignee: |
Imperial Chemical Industries
Limited (London, EN)
|
Family
ID: |
10472678 |
Appl.
No.: |
05/272,498 |
Filed: |
July 17, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Nov 26, 1971 [UK] |
|
|
55001/71 |
|
Current U.S.
Class: |
427/383.5;
987/300; 428/418; 428/450; 428/462; 427/428.01; 427/427.7; 427/429;
427/427; 427/430.1; 428/430; 428/458; 987/27 |
Current CPC
Class: |
C01B
25/26 (20130101); C01B 25/455 (20130101); C03C
13/00 (20130101); C03C 17/25 (20130101); C03C
17/256 (20130101); C03C 25/38 (20130101); C04B
28/342 (20130101); C04B 41/88 (20130101); C07F
9/02 (20130101); C07F 9/66 (20130101); C09D
1/00 (20130101); C09D 5/32 (20130101); C23C
22/03 (20130101); C03C 2217/23 (20130101); C03C
2218/11 (20130101); Y10T 428/31696 (20150401); Y10T
428/31529 (20150401); Y10T 428/31681 (20150401); Y10T
428/31616 (20150401) |
Current International
Class: |
C01B
25/455 (20060101); C01B 25/00 (20060101); C04B
28/00 (20060101); C04B 28/34 (20060101); C01B
25/26 (20060101); C09D 5/32 (20060101); C23C
22/03 (20060101); B27K 3/52 (20060101); C07F
9/00 (20060101); C07F 9/02 (20060101); C07F
9/66 (20060101); C23C 22/02 (20060101); C03C
13/00 (20060101); C04B 41/88 (20060101); C09D
1/00 (20060101); C03C 25/38 (20060101); C03C
25/24 (20060101); C03C 17/25 (20060101); B05D
003/04 (); B32B 015/08 () |
Field of
Search: |
;117/138.8D,138.8E,138.8F,138.8R,16R,139.5CF,169R,94,95,138,151,33.3
;252/8.6 ;106/1,15FP,286 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Willis, Jr.; P. E.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What we claim is:
1. A method of applying a continuous coating consisting essentially
of a metal phosphate to the surface of an organic polymer article
comprising applying to the surface a liquid composition containing
a solution of
a. a compound of a metal selected from the group consisting of Mg,
Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo,
Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pb, Au, Hg, Th
and U; and
b. an oxyacid of phosphorus or a compound capable of forming such
an oxyacid in the solution, the oxyacid being an ortho- or
meta-acid of the structure (1) ##EQU5## Where X.sup.1 and X.sup.2
are the same or different and selected from hydrogen, hydroxyl,
halide or which have the structure (2) to provide pyrophosphoric
acid ##EQU6## wherein the solvent is a solvent for both components
(a) and (b) and contains an organic component and the atomic ratio
of metal to phosphorus is in the range 1:0.1 to 1:2.9 and
converting the coating so formed to a metal phosphate by air-drying
or by heating to give a coating of 0.01 to 5 microns thickness.
2. A method as claimed in claim 1 in which the composition is
applied by dip-coating, spraying, or by roller- or
brush-coating.
3. A method as claimed in claim 1 in which the metal compound
comprises an iron compound and the oxyacid of phosphorus is
orthophosphoric acid.
4. A method as claimed in claim 1 in which the metal compound
comprises a mixture of an iron and titanium compound.
5. A method as claimed in claim 3 in which the organic polymer is
in the form of a sheet or film.
6. A method as claimed in claim 3 in which the organic polymer is a
polyester.
7. A method as claimed in claim 6 in which the polyester is
poly(ethylene terephthalate).
8. A method as claimed in claim 3 in which the organic polymer is
polypropylene.
9. A method as claimed in claim 1 in which the coating applied to
the organic polymer is heated at a temperature of 30.degree.C. to
120.degree.C. to form the metal phosphate.
Description
This invention relates to coatings on organic polymers of chemical
compositions of metals and complexes isolatable therefrom,
particularly coatings of compositions and complexes containing
organic ligands and ligands derived from oxyacids of phosphorus of
arsenic. The compositions and complexes and their preparation are
described in the co-pending U.S. patent application of Colebourne
and Rolfe Ser. No. 272458, assignors to Imperial Chemical
Industries Limited, which is based on U.K. Patent Applications
34012/71 and 58999/71.
Metals, for the purpose of the present specification, are defined
as the elements of the periodic table of elements, having an atomic
number of 12, 14, 20 to 32, 39 to 50, 56 to 80, 90 or 92. By an
oxyacid of phosphorus or arsenic we mean a phosphorus or arsenic
compound containing the group of structure (1) ##EQU1## where Z is
a phosphorus or arsenic atom, X.sup.1 and X.sup.2 are the same or
different and selected from hydrogen, hydroxyl and halide, or, when
Z is phosphorus, X.sup.2 may have the structure (2) to provide
pyrophosphate ##EQU2##
These oxyacids and ligands derived therefrom are referred to as
phosphate and arsenate: within the term are included the
meta-phosphate and arsenate and pyrophospate.
The invention has several aspects and these will be described under
the following heading E. For convenience details of the
compositions and complexes are also given under headings A to
D.
A-- the compositions
B -- complexes isolatable therefrom
C -- methods of preparing complexes
D -- properties of the complexes and their solutions
E -- uses of the compositions and complexes in forming coatings
F -- examples of products and processes under heading E
A. The Compositions
Our invention uses liquid metal-containing compositions which
comprise a solution, in an at least partly organic, preferably
oxygen-containing, solvent, of (a) a metal compound and (b) an
oxyacid of phosphorus or arsenic or a compound capable of forming
such an oxyacid in the solution. These compositions are capable of
decomposing on heating to a metal phosphate or arsenate.
The organic solvent is preferably selected from alcohols, esters,
ketones, aldehydes, nitro compounds and ethers, especially
monohydric alcohols, ROH containing 1 to 10 carbon atoms, esters of
the structure R.sup.1 COOR.sup.2 where R, R.sup.1 and R.sup.2 are
alkyl groups or substituted alkyl groups containing from 1 to 10
carbon atoms each, ethers of the structure R.sup.1 OR.sup.2 and
ketones of the structure R.sup.1 COR.sup.2, where R.sup.1 and
R.sup.2 have the meaning ascribed above, nitro compounds of the
structure R.sup.1 NO.sub.2 and ethers of the structure OR.sup.3
where R.sup.3 is a divalent alkyl group having from 4 to 7 carbon
atoms one of which may be replaced by an oxygenation. Mixtures of
one or more solvents may be used. Diluents may also be present,
provided they do not bring about precipitation of the components of
the composition. Up to 50% of aromatic or halogenated hydrocarbon
diluents may be present. The effect of including larger amounts of
such diluents will be discussed in detail later.
While phosphate and arsenate are used in this specification to
cover oxyacids of phosphorus or arsenic in general, orthophosphate
and orthoarsenate are preferred.
The metal-containing composition may be formed by dissolving a
complex of the type described in Section B of this specification in
a solvent. Alternatively a metal compound and an oxyacid of
phosphorus or arsenic (or a source thereof, such as the acid
anhydrides or an oxyhalide) are dissolved in a solvent for at least
one component and the reaction product in the presence of organic
ligands. The metal compound may be a phosphate or arsenate and so
provide the oxyacid of phosphorus or arsenic, in which case an
additional acid may be required, e.g. hydrochloric or nitric
acid.
A wide range of metal compounds may be used. Simple inorganic salts
including oxides and hydroxides are suitable, such as halides,
carbonate, nitrate, phosphate, perchlorate and cyanate. Sulphates
may be used in some applications but they can be disadvantageous
for some purposes owing to the difficulty with which they are
thermally decomposed.
Also suitable are salts of organic acids such as acetates,
benzoates, oxalates, propionates or formates. Alkoxides are also
useful.
Alternatively co-ordination complexes of the metal may be used, for
example complexes having ligands derived from acetylacetone,
ethylenedithiol, ethanolamine, carbon monoxide or phosphines.
Mixtures of metal salts and ligand-forming reagents may be used.
Also, two or more salts or complexes of the same or different
metals may be used, if desired.
The preparation of compositions containing a wide range of metals
will be described in detail later.
The solvent is selected from the wide range of organic solvents
which dissolve the components of the composition. Aliphatic
alcohols containing 1 to 10 carbon atoms are particularly
convenient, especially lower molecular weight alcohols containing 1
to 4 carbon atoms, for example methanol, ethanol, n- or
iso-propanol and substituted alcohols especially methoxy- or
ethoxy-ethanol. Suitable esters are ethyl acetate or carbonate.
Acetyl acetone may be used. Tetrahydrofuran is the most preferred
ether to use, though dioxan may also be used. Aromatic hydroxy
compounds can be used, but solubility is low in such materials.
The reactants used may be brought together in any desired order,
but we prefer to add the oxyacid or a precursor thereof to the
metal compound dissolved or suspended in the organic solvent.
We prefer to prepare compositions in which the metal and oxyacid
are present with atomic ratios of metal to phosphorus or arsenic
from 1:0.1 to 1:2.9 more preferably 1:0.5 to 1:2.
The composition may be prepared over a wide range of temperatures,
for example from 50.degree.C to 150.degree.C, but generally we
prefer to mix the components at temperatures below about
60.degree.C. The process may, if desired, be carried out at
pressures above normal atmospheric pressure, but it is found that,
generally, if the temperature is kept below the normal boiling
point of the solvent, such excess pressure is not needed.
For optimum product yield and purity all the steps in the
preparation including any preparatory operations are preferably
carried out under conditions in which little additional water is
introduced apart from that provided by the components such as water
of crystallisation from metal compounds or water from phosphoric
acid. It is not essential, however, to maintain anhydrous
conditions; in fact up to about 25% by weight of the composition
may be water, though the precise upper limit depends on the choice
of solvent and metal concentrations and is best determined by small
scale trial.
Additional components such as pigments, polymers, colourants,
surfactants or sources of other ions and other additives may be
included in the compositions, but since the purpose of the
additional component is related generally to uses of the
composition, detailed discussion will be deferred until a later
section.
The liquid compositions may be converted into dry compositions by
removal of the solvents, provided the compositions are maintained
in an atmosphere of the solvent. Spray-drying is a convenient
technique for producing solids. These may be redissolved in
suitable solvents of the type described to reconstitute the liquid
composition.
The solubility of our compositions in organic solvents is due to
complex formation. These complexes may be isolated and their nature
and typical properties will now be described.
B. The Complexes
Our invention may also use metal-containing complexes in which
there is associated with a metal ion one or more phosphate or
arsenate ligands and one or more organic ligands, the organic
ligands being derived from organic compounds containing an
electron-donating oxygen atom or their thio-equivalents. The most
commonly used organic compounds for this purpose are hydroxyl
compounds, especially alcohols; carbonyl compounds including
aldehydes, ketones and esters; nitro compounds and ethers including
cyclic ethers. Of particular importance because of their ready
availability are lower monohydric alcohols ROH containing 1 to 10
carbon atoms, esters of the structure R.sup.1 COOR.sup.2 where
R,R.sup.1 and R.sup.2 are alkyl groups or substituted alkyl groups
containing from 1 to 10 carbon atoms each, ethers or ketones of the
structure R.sup.1 --O--R.sup.2 or R.sup.1 --CO--R.sup.2 nitro
compounds of the formula R.sup.1 NO.sub.2, where R.sup.1 and
R.sup.2 have the meaning ascribed above, and ethers of the
structure OR.sup.3 where R.sup.3 is a divalent alkyl group having
up to 7 carbon atoms one of which may be replaced by a oxygen
atom.
The complexes are difficult to characterise structurally because
some of the liquids are rather labile but the evidence which will
be discussed indicates the presence of complex ions of the
structure (4) in cases where the metal has a valency of m and
co-ordination number of 6 or more. ##EQU3## or where the
co-ordination number is four, the equivalent complex ion is of the
structure ##EQU4##
In formulae (4) and (5) L.sup.1 and L.sup.2 represent other
ligands, at least one of which in a given ion is an organic ligand.
L.sup.1 and L.sup.2 may be also inorganic ligands, such as halide,
sulphate, nitrate or thiocyanate, when corresponding adjustment of
the total valency of the ion will have to be made. Complexes may
contain more than one unit of structure (4 to 5) linked together
through hydrogen bonding of organic ligands L.sup.1 and L.sup.2 :
also at least one but not all of ligand pairs L.sup.1 and L.sup.2
may be replaced by bidentate groups such as phosphate groups. Such
an ion is difficult to represent in two dimensions but a
complicated structure of this type containing additional phosphate
ligands accounts for the analyses of certain complexes of the
invention containing trivalent metals having a metal to phosphorus
ratio in the range 1:1 to 1:2.9.
Q is a metal of atomic numbr 12, 14, 20-32, 39-50, 57-80, 90 or 92,
having a valency m and a co-ordination number of 4.
The counter ion associated with the anions described above may be
selected from a wide range of cations but is usually hydrogen
(H.sup.+) or M.sup.m.sup.+ or Q.sup.m.sup.+.
The complexes may be characterised in several further ways. Heating
the solid decomposes it to a metal phosphate and a distillate is
obtained which consists mainly of an organic compound corresponding
to the co-ordinated organic liquid.
Proton magnetic resonance studies on alcoholic solutions of the
complexes show a shift of resonance to a field high of the usual
proton resonance range and the resonance is broadened. For example
an iron complex in methanol shifts the resonance 30 ppm high. That
the complexes are not strongly bound together is indicated by the
observation of only a single signal for solvent and ligand
methanol, suggesting rapid exchange.
Infra-red or laser-Raman spectroscopy may be used to characterise
the complex and to identify the presence of phosphate groups (about
900-925 cm.sup.-.sup.1 and 1088 cm.sup.-.sup.1) and the organic
ligand. Compared with the organic compound from which the ligand is
derived the peaks in the spectrum of the complex often show a shift
(in one or other direction) of 3-12 cm.sup.-.sup.1, suggesting weak
coupling.
Ultra-violet spectroscopy may be used to characterise the
environment of the metal, conveniently by evaporating a solution of
the complex on a quartz plate and measuring ultra-violet
transmission over the range 200 to 450 millimicrons. In the
examples at the end of this specification ultra-violet
characteristics of complexes of a number of metals will be
described in detail.
C. Methods of Preparing Complexes
Several methods will be described, all of which have in common the
feature of bringing together, in a solvent for at least one
component or the product complex, a source of an oxyacid of
phosphorus or arsenic, a source of metal ions and a source of
organic ligands. Conveniently the source of organic ligands is the
solvent or part of the solvent. The differences between the several
processes described are mainly in connection with the method of
isolating the product complex from the compositon. For any given
solvent or mixture of solvents, the process conditions can be
adjusted either to maintain the complex in solution, or to
precipitate it, according to whether its solubility product is
exceeded. Precipitation can be achieved, for example, by selection
of the solvent, by concentration, by altering the temperature
and/or pressure, or by addition of a further component in which the
complex has a low solubility. For some purposes however such
isolation is not necessary, for the compositions may be used as
prepared. Since the organic ligands are usually rather labile, if
the isolated complex is to be stored, it should be maintained in an
atmosphere of the ligand source, i.e. the organic solvent which
provides the ligand.
According to a first process for preparing a complex for use in our
invention, an oxyacid of phosphorus or arsenic or a source thereof,
a metal compound and a source of organic ligands are brought
together in an organic medium which is capable of dissolving the
components, but in which the solubility product of the resulting
complex is exceeded. The complex phosphate or arsenate produced may
be isolated for example by filtration, decanting off the remaining
liquid or by centrifuging. The product may be dissolved in another
solvent, e.g. an alcohol, for use.
Suitable organic media for this process include ethers, preferably
cyclic ethers, esters, alcohols, ketones, nitro-compounds, amides,
carbonates, sulphones, sulphoxides and mixtures of such solvents.
Examples of such suitable solvents are tetrahydrofuran, dimethyl
sulphoxide, ethylene carbonate, propylene carbonate, acetone,
methyl ethyl ketone, methyl acetate, n-propyl alcohol, n-butyl
alcohol, ethyl acetate, nitromethane, ethyl acrylate and diethyl
carbonate.
The reactants used may be brought together in any desired order,
but we prefer to add the oxyacid, or a precursor thereof, to the
metal compound dissolved in the organic medium.
In this case the oxyacid, or precursor thereof is added directly or
in solution to a solution of the metal compound, to precipitate the
complex.
According to a second process for preparing a complex for use in
our invention, a metal compound, a source of organic ligands and
the oxyacid of phosphorus or arsenic or precursor thereof, are
dissolved in a solvent for the components and the reaction product,
then the complex is separated by adding a phase separator to the
reaction mixture.
The phase separator is an organic substance which is miscible with
the solvent used but in the presence of which the solubility
product of the complex is exceeded. Thus the complex separates out
as a solid or as an oil.
The phase separator is preferably a substance having a low
dielectric constant, especially a dielectric constant from 2 to 11.
Most preferred phase separators have a low co-ordinating power for
the metals of the compounds used in the process. It is usual for
the phase separator to be a liquid at the temperature at which the
process is carried out; preferred liquids are hydrocarbons and
halogenated derivatives, for example methylene chloride,
trichloroethylene, carbon tetrachloride, chloroform, ethylene
dichloride, methyl chloroform, chlorobenzene, toluene, xylene,
benzene or C.sub.6 to C.sub.12 aliphatic hydrocarbons. Certain
organic liquids can act as co-ordinating ligands or as phase
separators. For example, in the presence of methanol as principal
solvent and organic ligand source, diethyl ether may act as a phase
separator. In the absence of a solvent of such high co-ordinating
power as methanol, diethyl ether may act as a co-ordinating
solvent. Best results therefore require a certain amount of
straightforward trial. Some degree of concentration of the solution
may be required e.g. evaporation under low pressure, before the
phase separator is added.
Reaction conditions of temperature, pressure and metal to
phosphorus ratio are generally as described above in connection
with the compositions.
D. Properties of Compositions, Complexes and their Solutions
A particular property of these materials which makes them useful
for many technical purposes is their ability to decompose to mainly
amorphous metal phosphates which are highly insoluble in solvents
for the original composition. In essence the composition is heated
to remove any solvent which remains and also the co-ordinate
organic ligands which are responsible for conferring solubility on
the complex. Further heating may be advantageous in removing bound
water to give greater insolubility.
When a complex has been isolated, it is preferably dissolved as
prepared, or in at least partly purified form, in a suitable
solvent before decompositon. A suitable solvent may conveniently be
selected from the organic co-ordinating solvents used in the
preparation of a composition or complex. Some water may be present,
provided the complex remains in solution.
Useful protic solvents are for example, methanol, ethanol,
cyclohexanol, n-propanol, benzyl alcohol and especially methanol.
Higher alcohols, substituted alcohols, polyfunctional alcohols and
aromatic alcohols, for example butanol, 2-methoxy-ethanol,
2-ethoxy-ethanol, 2-butoxy-ethanol, trichloroethanol,
trifluoroethanol, bromomethanol, ethylene glycol, glycerol and
cresol may also be used as solvents. Aprotic solvents may also be
used, for example tetrahydrofuran, N,N-dimethyl formamide, N-methyl
pyrrolidone, N,N-dimethyl acetamide, dimethyl sulphoxide, ethylene
carbonate, propylene carbonate, acetone, methyl ethyl ketone, ethyl
acetate, methyl acetate and nitromethane. Especially useful solvent
mixtures are derived from methanol or ethanol and a chlorinated
hydrocarbon, for example, chloroform, methylene chloride, ethylene
dichloride and trichloroethylene; from methanol and methyl ethyl
ketone or tetrahydrofuran; from methanol and dimethyl formamide;
from methanol and chloral hydrate and from methoxy- or
ethoxy-ethanol and toluene.
Decompositon of the composition is preferably carried out by
heating or by air-drying at room temperature, optionally under
reduced pressure.
Heating may be carried out at comparatively low temperatures, for
example from 30.degree. to 120.degree.C, to form the phosphate or
arsenate of the metal. Stronger heating, for example at
temperatures greater than 150.degree.C up to 1000.degree.C, can
produce a phosphate or arsenate of the metal of somewhat different
composition, due it is believed, to condensation and cross-lining.
The duration of heating varies over a wide range depending upon the
particular compositon and the desired end-product and is typically
from practically instantaneous, as when a solution is sprayed onto
a hot surface, up to 100 hours.
E. Uses of Compositions and Complexes in Forming Coatings
A composition, including a complex or a solution of a complex of
the type described, may be used to coat organic polymer substrates
by applying it to the substrate and subsequently allowing it or
causing it to decompose to form an insoluble coating of the
phosphate or arsenate of the metal, the coating being in the range
0.01 to 5 microns thick. The substrate may take up a variety of
shapes, e.g. fibre, filament, sheet, granule, powder or
cenospheres. The substrate may be coated with or impregnated with
solution. The coatings are usually non-crystalline. A complex metal
phosphate for use in the invention can be used to produce
heat-stable, inert, transparent, hard films of a phosphate of a
metal, especially films of the phosphates of iron, titanium,
vanadium or chromium. Coatings of phosphate may be prepared in
relatively thick layers for each application of coating solution.
Ferric phosphate and titanium phosphate and mixtures of the two
have useful ultraviolet radiation absorbing properties; chromium
phosphate is useful when coated on polymers to enhance the water
and alkali-resistance of the glass. We have found that coatings of
thickness in the range 0.01 to 3 microns, preferably 0.2 to 2.5
microns give the best results. Thick coatings may be produced by
repeated coatings, with or without conversion to phosphate between
each stage. Mixtures of two or more metals may be present in the
compositions. Aluminium compounds may also be present.
A convenient method for applying the coating comprises dip-coating,
spraying, powder-, roller- or brush-coating the substrate to be
coated with a compositon or solution of complex according to the
invention, removing part or all of any organic solvent, then
decomposing the complex to yield a phosphate, at a temperature from
room temperature up to 1000.degree.C or such lower temperature than
1000.degree.C that is set by the maximum temperature which the
substrate to be coated can withstand without damage or loss of
useful properties. Of course, if at the same time as decomposing
the phosphate, thermal modification of the substrate is planned,
then the temperature may be set accordingly.
The coating solution may include additional components, for example
materials which will aid the further processing of the solutions or
desirably affect the properties of the coatings formed from the
solutions. Thus organic materials, especially polymers or monomers,
may be dissolved in the complex solution given an appropriate
solvent. Examples of suitable polymers include diene polymers,
acetylene polymers, vinyl and vinylidene polymers, e.g. acrylic
acid and methacrylic polymers, acrylate and methacrylate polymers,
polyacrylonitrile, polyethers, polysulphones, formaldehyde resins,
polyesters, polycarbonates, polyamides, polyureas and
polyurethanes, natural polymers and modified natural polymers and
polysiloxanes. Copolymers or terpolymers of the monomers of the
aforementioned may also be used. In some cases it will be
convenient to dissolve the corresponding monomer in the complex
solution and polymerise it later, for example simultaneously with
the thermal decomposition of the complex. It will be understood
that a suitable solvent or solvent mixture has to be chosen which
will dissolve both the complex and the polymer.
Additional components, for example pigments, colourants,
surfactants, plasticisers, antioxidants, heat stabilisers
ultra-violet stabilisers, or fillers such as metal powders may also
be dispersed in the composition. Additional compounds which may be
introduced include materials which can control the chemical or
physical nature of the solid phase of metal phosphate which is
produced from the solution. Thus a boric acid ester or ether or a
silicic acid ester or ether (for example methyl borate, trimethoxy
boroxine or ethyl silicate) may be introduced to suppress the
crystallisation of the metal phosphate.
The ultra-violet absorption properties of the coatings may be
enhanced by introducing a compound of another metal. It is
especially preferred to incorporate, for this purpose, a compound
of chromium, iron, titanium or of a manganese which is soluble in
the particular solvent used. Thus, for example manganese(II),
Iron(III), or titanium(III) or (IV) or chromium(III) may be
incorporated in the solution from which the coating is formed.
The ultra-violet absorption properties of the coating may also be
enhanced by introduction of organic compounds which themselves
absorb in the ultra-violet, for example benzophenones and
benzotriazoles. When the solubility of the organic compound allows,
it may be dissolved in the solution from which the coating is
formed; alternatively the organic compound may be introduced in
particulate form by slurrying with the solution of the complex. If
desired, both transition metals and organic compounds may be
introduced into a single coating.
The chemical resistance of the coatings may similarly be enhanced
by the introduction of compounds of other metals for example tin or
calcium or a boron compound. Aluminium phosphate precursors may
also be present.
The coatings may be used to modify the surface energy of the
substrate to give hydrophilic or hydrophobic coatings.
The refractive index of the coatings may be modified as desired by
the incorporation of metal compounds or organic polymers.
In certain applications particulate solids may usefully be
dispersed in the solutions of the complex as for example,
refractory materials such as silica, or metal oxides including
titania and zirconia may be so dispersed to produce, on
decomposition of the complex, a metal phosphate coating containing
refractory materials. Thus the inclusion of graphite is useful in
producing an electrically-conducting metal phosphate. Solid-phase
lubricants such as graphite, molybdenum sulphide, poly(carbon
monofluoride) and polytetrafluoroethylene, may be present.
Metal phosphate coatings may advantageously be employed as coatings
for a wide variety of natural and synthetic organic polymeric
substrates. Natural polymers which may be coated include cellulosic
polymers and materials derived therefrom, for example wood and
paper. Synthetic polymers which may be coated include polyolefins
(for example polymers and copolymers of ethylene, polypropylene,
butadiene, isoprene, 4-methyl pentene-1 and styrene), copolymers of
ethylene with unsaturated esters (for example with vinyl acetate or
alkyl acrylates or methacrylates), modified polystyrene copolymers
(for example a styrene-maleic anhydride and styrene-acrylonitrile
copolymer), polymers and copolymers of other
ethylenically-unsaturated monomers (for example vinyl chloride,
vinylidene chloride, chloroprene, methyl methacrylate, ethyl
acrylate and vinyl acetate), polyphenylene oxides and sulphides,
polysulphones, polyoxymethylenes, polyamides, (for example
polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 6-6)
and polyundecanolactam (nylon 11 ), and polycarbonates and
polyesters (for example polyethylene
1,2-diphenoxyethane-4,4'-dicarboxylate and polyethylene
terephthalate).
A coating of the phosphate complex may be applied to the polymeric
substrate by a variety of techniques, for example by dipping,
spraying or by roller-, brush- or powder-coating. The coating may
be deposited in a single coating operation or in a succession of
such operations, depending upon the thickness desired, the
concentration and composition of the solution of the complex
employed, and the conditions employed in the deposition of the
initial coating and in its subsequent decomposition to yield the
phosphate. It will be understood that the permissible temperature
of decomposition will depend upon the particular substrate to be
coated, and the susceptibility of the substrate to deformation or
degradation will be very important in guiding the choice of
decomposition conditions.
In utilising the ultra-violet absorption characteristics of the
coatings of iron phosphate on polymeric materials it is preferred
to use a coating at least 0.4 micron in thickness since the use of
thinner coatings (for example coatings less than 0.2 micron in
thickness) may accelerate the photodegradation of the polymeric
substrate. The acceleration of the photodegradation may in fact,
find useful practical application in the coating of certain
plastics materials, especially materials used in packaging (e.g.
plastics films or containers) when it is desired to overcome the
problems posed by disposal of non-degradable waste materials,
especially polypropylene and polyvinyl chloride. The mechanism of
the acceleration of photodegradation is not fully understood but as
the thickness of the coating is increased this effect appears to be
overwhelmed by the effect of increased ultra-violet absorption by
the thicker coating. Whichever effect is desired in a particular
application, the optimum thickness will depend, for example, upon
the particular polymeric substrate and upon the effect of any other
components which may be incorporated in the iron phosphate
coating.
For use in applications where anti-static properties are desirable
considerations similar to those described for glass substrates
apply.
Polymeric substrates coated with phosphate coatings find
application in a wide variety of contexts and the substrates may
take various forms, for example sheets, tapes and other shaped
articles.
The phosphate or arsenate coating may form a primer or anchor
coating for the surface of paper or plastics material which is to
be painted, printed or metallised, or further coated with one or
more phosphate or arsenate coatings.
The gas and water impermeability of the phosphate coatings is
especially advantageous in the coating of plastics materials, for
example films or containers, for use in packaging of foodstuffs.
The abrasion resistance of the coatings may be utilised, for
example, in the coating of plastics tapes (for example polyester
tapes) and rigid sheets such as polymethylacrylate and
polystyrene.
The ultra-violet absorption characteristics of iron phosphate
coatings may be utilised in applications where rigid plastics
sheets or formed bodies are intended for use under conditions of
intense illumination, for example in light-shades especially
light-diffusers for use in conjunction with fluorescent tubes. The
coatings may also be used to reduce ultra-violet degradation of
wood, for outdoor use.
The invention is illustrated but not limited by the following
Examples:
EXAMPLE 1
A filtered solution of anhydrous ferric chloride (350 g) in
"Analar" grade methanol (255 ml) was treated at room temperature
with 131 ml of 88% orthophosphoric acid. The mixture was then
stripped of excess methanol by means of a rotary evaporator, and
the residual liquor stripped further under dynamic vacuum. The
distillate from this stripping contained a large quantity of
hydrogen chloride. The syrupy concentrate was then treated at room
temperature with three times its volume of methylene chloride and
shaken vigorously. The white solid complex derivative obtained at
this stage was filtered off and washed free of soluble iron (as
HFeCl.sub.4) with methylene chloride. The residual solid was
dissolved in methanol to give a viscous solution (Solution A)
containing, by weight, 12.0% Fe and 14.0% P corresponding to an
atomic ratio Fe/P = 1/2.1.
A portion of Solution A was diluted with methanol to give a
solution containing, by weight, 4.1% Fe (Solution B).
A sample of polyester sheet ("Melinex" polyethylene terephthalate)
6 cm square and 25 microns thick was coated with the complex iron
phosphate derivative by dipping in a portion of Solution B, the
sheet being withdrawn from the solution at the rate of nine inches
per minute. This coating was dried in a stream of nitrogen at
ambient temperature for 15 minutes and then "cured" by heating at
120.degree.C for 30 minutes to yield the final coating of an iron
phosphate. The thickness of the iron phosphate coating on each side
of the polyester sheet was 0.4 micron.
The permeability of the coated sheet was measured at 27.degree.C
and 76.9 cm Hg after degassing for twelve hours under reduced
pressure. The total permeability of the coated polyester sheet was
found to be 2.3 .times. 10.sup.-.sup.20 mole meter
Newton.sup.-.sup.1 sec.sup.-.sup.1, corresponding to the value of
6.1 .times. 10.sup.-.sup.22 mole meter Newton.sup.-.sup.1
sec.sup.-.sup.1 for the permeability of the iron phosphate
coating.
By way of comparison the total permeability of an uncoated sample
of the same polyester sheet measured under the same conditions was
3.1 .times. 10.sup.-.sup.18 mole meter Newton.sup.-.sup.1
sec.sup.-.sup.1.
EXAMPLE 2
A portion of Solution A (as described in Example 1) was diluted
with methanol to give a solution containing, by weight, of 6.0% Fe
(Solution C).
Solution C was used to coat a sample of polyester sheet ("Melinex"
polyethylene terephthalate) 6 cm square and 100 microns thick by
the procedure described in Example 1. The coating was dried and
"cured" as described in Example 1 and the thickness of the iron
phosphate coating on each side of the polyester sheet was 1.2
micron.
The total permeability of the coated polyester sheet was found to
be 4.3 .times. 10.sup.-.sup.19 mole meter Newton.sup.-.sup.1
sec.sup.-.sup.1, corresponding to the value of 9 .times.
10.sup.-.sup.21 mole meter Newton.sup.-.sup.1 sec.sup.-.sup.1. for
the permeability of the iron phosphate coating.
EXAMPLE 3
A portion of Solution A (as described in Example 1) was diluted
with methanol to give a solution containing, by weight, 2.0% Fe
(Solution D).
Solution D was used to coat a sample of polypropylene sheet 6 cm
square and 24 microns thick by the procedure described in Example
1. The coating was dried and "cured" as described in Example 1
except that the "curing" was carried out at a temperature of
90.degree.C for 150 minutes. The thickness of the iron phosphate
coating on each side of the polypropylene sheet was 0.15
micron.
The total permeability of the coated polypropylene sheet was found
to be 2.4 .times. 10.sup.-.sup.18 mole meter Newton.sup.-.sup.1
sec.sup.-.sup.1, corresponding to the value of 3 .times.
10.sup.-.sup.20 mole meter Newton.sup.-.sup.1 sec.sup.-.sup.1 for
the permeability of the iron phosphate coating.
EXAMPLE 4
Another sample of polypropylene sheet (as described in Example 3)
was coated using the procedure described in Example 3 except that a
second layer of the coating was applied by repetition of the
coating, drying and "curing" process. The thickness of the iron
phosphate coating on each side of the polypropylene sheet was 0.3
micron.
The total permeability of the coated polypropylene sheet was 9.3
.times. 10.sup.-.sup.19 mole meter Newton.sup.-.sup.1
sec.sup.-.sup.1, corresponding to the value of 6.2 .times.
10.sup.-.sup.21 mole meter Newton.sup.-.sup.1 sec.sup.-.sup.1 for
the permeability of the iron phosphate coating.
EXAMPLE 5
Solution B (as described in Example 1) was used to coat strips of
"Darvic" rigid polyvinyl chloride sheet 41/2 inches long and 1 inch
wide by the procedure described in Example 1 except that only
one-half of the area of each strip was coated. The thickness of the
iron phosphate coating on each side of the coated portion of each
strip was 0.4 micron.
The strips were then subjected to the radiation from a "Hanovia"
U.V. 500 mercury arc lamp, the strips being placed at a distance of
about eight inches from the lamp. After exposure of the radiation
for five hours, the coated portions of the strips had acquired a
very slight brown colouration whereas the uncoated portions had
become darker brown and chalky in appearance.
EXAMPLE 6
4.6 g of manganous chloride hydrate (MnCl.sub.2.2H.sub.2 O) were
added to 100 g of Solution B (as described in Example 1) to give
Solution E.
Solution E was used to coat strips of "Darvic" rigid polyvinyl
chloride sheet by the procedure described in Example 1, except that
only one-half of the area of each strip was coated and that
"curing" was carried out at 70.degree.C for 30 minutes. The process
of coating, drying and "curing" was repeated and the thickness of
the final coating on each side of the coated portion of each strip
was 0.8 micron.
The strips were subjected to the radiation from a mercury arc lamp
as described in Example 5. After exposure to the radiation for five
hours, the coated portions of the strips had retained their
positive colourless appearance whereas the uncoated portions had
become brown and chalky in appearance.
EXAMPLE 7
A portion of Solution A (as described in Example 1) was diluted
with methanol to give a solution containing, by weight, 1.0% Fe
(Solution F).
Solution F was used to coat strips of "Darvic" polyvinyl chloride
sheet by the procedure described in Example 5. The thickness of the
iron phosphate coating on each side of the coated portion of each
strip was 0.1 micron. The strips were subjected to the radiation
from a mercury arc lamp as described in Example 5. After exposure
to the radiation for three hours the coated portions had become
very dark brown relative to the uncoated portions, thus
illustrating the effect of acceleration of photodegradation brought
about by thin coatings of the iron phosphate.
EXAMPLE 8
A portion of Solution A (as described in Example 1) was diluted
with methanol to give a solution containing, by weight, 1% Fe
(Solution G).
A sample of polyester sheet ("Melinex" polyethylene terephthalate)
6 cm square and 25 microns thick was coated with the complex iron
phosphate derivative using Solution G by the procedure described in
Example 1. The "curing" of the coating was carried out at
100.degree.C for three minutes. The thickness of the iron phosphate
coating on each side of the polyester sheet was 0.07 micron.
The surface resistivity of the coated sheet was measured at 60%
relative humidity, using a "Ultra Megometer" instrument, and was
found to be 1.4 .times. 10.sup.8 ohms/cm.sup.2. By way of
comparison, the surface resistivity of the uncoated polyester sheet
was more than 10.sup.16 ohms/cm.sup.2.
Further samples of the same polyester sheet were coated by the same
process, using methanol solutions containing different
concentrations of the complex iron phosphate derivative, giving
rise to coatings of different thicknesses. The surface resistivity
was measured, as follows:
Solution % Fe Thickness Surface by weight of coating resistivity
(microns) ohms/cm.sup.2 ______________________________________ H
1.5 0.10 9.5 .times. 10.sup.7 I 2.5 0.17 4.9 .times. 10.sup.7 J 5.0
0.45 1.2 .times. 10.sup.7
______________________________________
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